Optically active 1-benzyl-3-hydroxypyrrolidine or a derivative thereof represented by formula (III) is reacted to 2,6-dimethyl-4-(m-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid-3-(1-benzyl-3-pyrrolidinyl) ester-5-methyl ester (hereinafter referred to as YM-09730), which has recently been found to have characteristic pharmacological effects, such as an effect to increase coronary blood flow when directly administered into the coronary artery. Thus, the compounds of formula (III) have been expected to be useful as starting materials for pharmaceuticals (see JP-A-61-63652 (the term "JP-A" as used herein means an "unexamined published Japanese patent application")).
3-Hydroxypyrrolidine which is structurally similar to the optically active 3-hydroxypyrrolidine derivatives of formula (III) is an industrially useful compound long known as an intermediate for pharmaceuticals and agricultural chemicals. It has conventionally been synthesized by, for example, once obtaining 1-benzyl-3-hydroxypyrrolidine and heating it in an autoclave in a hydrogen gas atmosphere in the presence of a palladium catalyst to release toluene. Other known processes for preparing 3-hydroxypyrrolidine include a process comprising reaction of 4-amino-1,2-butanediol in the presence of a metallic catalyst (see JP-A-57-56457), a process comprising decarboxylation of 4-hydroxy-L-proline in the presence of cyclohexenone (see JP-A-60-23328), and a process comprising reacting a butane derivative represented by the formula: ##STR4## wherein X.sup.1 and X.sup.2, which may be the same or different, each represents an alkylsulfonyloxy group, a halogenoalkylsulfonyloxy group, an arylsulfonyloxy group, or a halogen atom, e.g., 2-hydroxy-1,4-di(methylsulfonyloxy)butane, with ammonia (see JP-A-60-104061).
Processes for synthesizing 1-benzyl-3-hydroxypyrrolidine, one of the aimed compounds of the present invention, which have been proposed to date include (1) a process comprising cyclizing dl-malic acid by reacting it with benzylamine to obtain 1-benzyl-3-hydroxysuccinic acid imide, which is then reduced with lithium aluminum hydride as described in Synthetic Communications, Vol. 13 (13), pp. 1117-1123 (1983); and (2) a process comprising reacting an alkyl 4-halo-3-hydroxybutyrate or an alkyl 3,4-epoxybutyrate with a benzylamine derivative to obtain a 1-benzyl-4-hydroxy-2-pyrrolidone derivative, which is then reduced with a reducing agent, e.g., lithium aluminum hydride, as described in JP-A-64-45360 and JP-A-1-207266.
From the fact that YM-09730 obtained via optically active (S)-(-)-1-benzyl-3-hydroxypyrrolidine as an intermediate is pharmacologically useful, a process for preparing (S)-(-)-1-benzyl-3-hydroxypyrrolidine has been proposed, in which optically active mandelic acid is added to a mixture of (S)-(-)-1-benzyl-3-hydroxypyrrolidine and a small proportion of by-produced (R)-(+)-1-benzyl-3-hydroxypyrrolidine which is obtained from (S)-(-)-malic acid according to the above-described process (1), to thereby crystallize a mandelic acid salt of (S)-(-)-1-benzyl-3-hydroxypyrrolidine, and the acid radical is then removed with an alkali, as disclosed in JP-A-61-63652.
However, each of the conventional processes for obtaining optically active 1-benzyl-3-hydroxypyrrolidine useful as an intermediate for pharmaceuticals involves problems. For example, naturally-occurring optically active compounds which are not easily available are used as a starting material as in the process (1); a step of cyclization followed by reduction is required, and lithium aluminum hydride which is not only difficult to handle on an industrial scale but expensive must be used as a reducing agent as in both processes (1) and (2).
In the light of these problems, it has been demanded to develop an economically advantageous process for obtaining optically active 1-benzyl-3-hydroxypyrrolidine derivatives useful as intermediates for pharmaceuticals, which process starts with an easily available optically active compound obtainable through, for example, synthetic procedures, and requires no complicated step.